ModSecurity - ModSecurity is an Open Source web application firewall developed by Trustwave's SpiderLabs.
Imperva SecureSphere - Get the flexibility, reliability, and performance you need to protect your business. SecureSphere covers you both on-premises or in the cloud.
AWS WAF - AWS WAF is a web application firewall that helps protect your web applications from common web exploits.
Barracuda Web Application Firewall - Barracuda Web Application Firewall offers security and DDoS protection against automated & targeted attacks.
Imperva Cloud Application Security - Deploy your applications and data where you want. When you want. Imperva keeps them secure in the cloud, on premises, and in hybrid clouds.
nginx - A high performance free open source web server powering busiest sites on the Internet.